| Abstract
| - Leucamide A (1), a bioactive cyclic heptapeptidecontaining a unique mixed 4,2-bisheterocycle tandem pairconsisting of a methyloxazole and thiazole subunit wasisolated together with the known compound BRS1 (2), fromthe dichloromethane extract of the Australian marine spongeLeucetta microraphis. The planar structure of leucamide A(1) was elucidated by employing spectroscopic techniques(NMR, MS, UV, and IR). Its absolute stereochemistry wasestablished by chemical degradation, derivatization, andchiral GC−MS analysis. A conformational analysis of 1 wasmade using MMFF. Leucamide A (1) was found to bemoderately cytotoxic toward several tumor cell lines.
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